Artificial wool



Patented June 23, 1942 ARTIFICIAL WOOL Vernal R. Hardy and John B.Miles, Jn, Wilmington, Del., assignors to E. I. du Pont de Nemours &Company, Wilmington, Del., a corporation of Delaware No Drawing.Application January 7, 1938, Serial No. 183,922

29 Claims.

This invention relates to artificial fibers and fabrics and moreparticularly to a new synthetic wool.

This application is a continuation-in-part of our application SerialNumber 125,939, filed l february 15, 1937.

In application Serial Number 125,940, filed February 15, 1937, by J. B.Miles, Jr., there are described unusual and valuable wool-like productsobtained by crimping filaments derived from synthetic linearcondensation polymers, particularly polyamides. The present invention isconcerned with a new process for crimping such filaments which isdistinguished from that disclosed in the above mentioned application inthat the crimping occurs spontaneously.

An object of this invention is to prepare cold drawn wet filaments whichwill crimp spontaneously when dried under low tension. A further objectis to prepare artificial wool-like filaments, fibers, yarns, fabrics,and the like. A further object is to prepare wool-like product havinggood strength, a high degree of crimp, good retentivity of crimp bothwet and dry, and good heat insulating properties. A still further objectis to prepare artificial fibers having a reversing helical crimp. Otherobjects will become apparent as the description proceeds.

These objects are accomplished by applying to suitably preparedfilaments of a synthetic linear condensation polymer a treatmentinvolving wetting with a mildswelling agent and cold drawing, as morefully described hereinafter, and then drying the cold drawn filamentsunder low tension, whereupon they crimp spontaneously, and if necessarysetting the crimp by suitable heat treatment.

The filaments to which our new crimping process is applied and fromwhich our new wool-like products are made, are derived from syntheticlinear condensation polymers of the type dethe polymers used and todefine certain terms and tests mentioned throughout the description. Aproperty of the fiber-forming synthetic linear condensation polymerswhich is especially utilized in this invention is their ability to bespun into filaments which can be cold drawn into oriented filaments. Theterm cold drawing is applied to the process of elongating the filamentswhile in the solid state by the application of stress. The cold drawnfilaments show definite orientation along the fiber axis whereas theundrawn filaments are substantially unoriented. The term filament asused herein will refer to both oriented and unoriented filaments orthreads which are drawn from the polymers regardless of whether thefilaments or threads are long (continuous) or short (staple), while theterm fiber will refer more specifically to the oriented filascribed inU. S. Patents 2,071,2502,071,253 and ments (long or short). The fibersare in general more useful in the manufacture of yarns and fabrics thanare the undrawn filaments. The term crimped filament or fiber will beused to indicate that the filament or fiber is not straight butpossesses a crinkled, curled, spiral, helical, or serrated form.

{The term intrinsic viscosity as applied herein to polymers is definedas in which m is the viscosity of a dilute m-cresol solution of thepolymer divided by the viscosity of m-cresol in the same units and atthe same temperature, and C is the concentration of polymer in grams percc. of solution. The intrinsic viscosity is indicative of the molecularweight of the polyamide. In the case of polyamides, polymers havingintrinsic viscosities between 0.6 and 1.5 are in general most suitablefor use in this invention. Polymers of the desired viscosity are bestprepared by heating the monomeric ingredients, e. g., a diamine and adicarboxylic acid, in the presence of a viscosity stabilizer, i. e., anagent which arrests the polymerization when a certain molecular weight(intrinsic viscosity) is reached. The point at which polymerizationceases is dependent upon the quantity of stabilizer used. Polymersprepared with the use of a viscosity stabilizer are essentiallyviscosity stable, i. e., they do not change materially in viscosity whenheated under melt spinningconditions. Suitable viscosity stabilizingagents for the preparation of polyamides are materials such as diamines,di-

carboxylic acids, or amide-forming derivatives of dibasic carboxylicacids, which may be included as excess reactant. Monofunctionalamide-forming compounds ,which include the nitrogenous bases, monobasiccarboxylic acids, and amide-forming derivatives thereof may also be usedas stabilizers. Sodium hydroxide, barium hydroxide, sodium acetate,ammonium acetate, etc. also function as viscosity stabilizers)Ethanolamine is also useful. The viscosity stabilizer is generally usedin amounts varying from 0.5 to 3.5 molar per cent based on thepolyamideforming reactants. Polymers prepared with the use of astabilizer or mixture of stabilizers will be referred to as viscositystable polymers.

' The term spontaneous crimping is applied to the operation in which thecrimp appears in the products of this invention. This operation consistsin drying in the relaxed condition suitably prepared cold drawn wetfilaments. It is referred to as spontaneous crimping because the crimpsappear spontaneously during the drying operation as-distinguished fromcrimps introduced by mechanical means or by other known methods ofcrimping.

The term setting as used herein will refer to any treatment whichimproved the permanency of the crimp in fibers. Setting usually takesthe form of heating the crimped fibers with steam.

As a means of evaluation and comparison, a test has been devised toindicate the degree of permanency of the crimp. This test consists inapplying a weight to the crimped fiber equivalent to 0.03 g. per denier(based on straightened length) and immersing the fiber inwater at 60 C.After 30 seconds immersion in water, the fiber is taken out, the loadremoved, and the fiber permitted to dry in the relaxed condition. Frommeasurements made during this test the crimp retentivity is calculatedin per cent by multiplying by 100 the quotient obtained by dividing thedifference between. the initial straightened length and recoveredcrimped length by the difference between initial straightened length andinitial crimped length. On the basis of this test the crimp retentivityof previously known artificial wools is quite low (below 40% andgenerally below 20%), whereas the crimp retentivity of the fibers hereindescribed is practically 100%.

For this reason a more severe test has been devised to show'up moreclearly differences between fibers produced by various modifications ofthe present invention. This test consists in stretching the crimpedfibers until the crimps are just straightened out and then applying anadditional stretch based on the length of the straightened fiber. Thefibers so stretched are immersed in boiling water for 30 seconds,removed, and allowed to dry in the relaxed condition. The crimp recoveryunder these drastic conditions, referred to as crimp recovery fromstretch, is expressed in per cent by multiplying by 100 the quotientobtained by dividing the difference between initial straightened lengthand recovered crimped length by the difference between initialstraightened length and initial crimped length. The crimp recovery fromstretch of previously known artificial wools is practically zero,whereas that of the polyamideder special conditions.

ethanol, propanol, isopropanol, or aniline.

As a result of this high crimp recovery the crimp is not lost when thefibers are made into fabrics whereas previously known artificial woolslose their crimp to a large extent during fabrication.

Having explained the various terms to be used, the invention will now bedescribed in detail and with particular reference to synthetic linearcondensation polyamides, since these polymers yield the mostsatisfactory artificial wool. The filaments used as starting materialmay be prepared from the polyamides by any method of spinning, e. g., bythe melt, dry, or wet processes. filaments of almost any diameter, butfilaments having deniers in the neighborhood of 0.5 to 20.0 areconverted into wool-like fibers with the greatest facility. Theinvention can be applied to single filaments or to a plurality offilaments. In the latter case the filaments may be twisted into a threadalthough this affects the nature of the crimp in the final product.

The characteristic feature of this invention is the spontaneous crimpingoperation. Two general procedures can be employed in making thefilaments susceptible to spontaneous crimping. One method consists insubjecting filaments regardless of their method of preparation to ashort heat treatment (conversion), preferably while wet with an agenthaving a mild swelling action on the filaments, and the other methodconsists in spinning the filaments from melt un- The second method is amodification of the first in which conversion is effected duringspinning. These methods will now be described in greater detail.

The first method, exemplified by subsequent Examples IIV, involves aheat pretreatment. This heat treatment is referred to as conversionbecause it converts the filaments into a form in which they aresusceptible to crimping. The conversion step is applied to thefilaments, either before or after the are partially cold drawn. Itconsists in heating the filaments for a short time in a suitable gas,vapor, or liquid.

Thus, heating in nitrogen at C. for 30 min-' utes, in steam at 150 C,for 3 minutes, or in oil at C. for one-half second are methods ofconversion. To obtain the best results the filaments should be wet witha liquid having a mild swelling action on the filaments under theconditions of conversion, e. g. water, methanol, If the filaments arehot wet when subjected to conversion, the subsequent cold drawingoperation must be applied after the filaments have been wetted with amild swelling agent, dried partially, and are in the process of dryingout. The preferred method of conversion is to wet the filament with ahydroxylated non-solvent for the polyamide, such as water, methanol,ethanol or isopropanol, prior to conversion and to pass the wet filamentrapidly through a bath of hot liquid. As examples of suitable liquidconversion media (baths) may be mentioned hydrocarbons; chlorinatedhydrocarbons; polyhydric alcohols, e. g. glycol and glycerol; esters, e.g. triacetin and castor oil; and ethers, e. g. the monobutyl ether ofdiethylene glycol. The conversion medium should be substantiallynon-volatile at the temperature and pressure used in conversion. It isdesirable to select a conversion medium which is not readily misciblewith the swelling agent with which the filaments are wetted and which iseasily removed from the filament by wash- Wool-like fibers can beprepared from fibers have been wetted, the drawing conditions,

ing or evaporation. Metals, e. g., mercury and molten Wood's metal, canalso be used as a conversion medium. Conversion can also be efiected bypassing the wet filaments through a heated slot or capillary. The slotor capillary must be of sufliciently small diameter to build upapres-Ysure of the vapor with which the filaments are wetted.

The temperaturev selected for conversion and the time of contact of thefilaments in the conversion medium will depend among other things on thenature of the liquid with which the filaments are wetted and the natureof the conversion medium. If conversion is to be efiected by passingwater-wet filaments through hot oil, the optimum temperature range ofthe oil will be 140 to 165 C. and the optimum time of contact will varyfrom about 0.5 second at th lower temperature to 0.2 second at thehigher temperature. On the other hand, if methanol-wet filaments are tobe converted by heating in tetrachloroethylene, the optimum temperaturerange for the conversion medium is 100 to 110 C. and the optimum time ofcontact is from about 0.4second at 100 C. to 0.2 second at 110 C. Colddrawn filaments undergo a high degree of shrinkage to 30%) duringconversion. For this reason it is necessary to adjust the rate at whichthe filaments are introduced into the conversion medium and removedtherefrom in order to compensate for this shrinkage.

Following conversion the conversion medium adhering to the filaments isremoved by washing or other suitable means. The filaments are then colddrawn.. If the filaments have been cold drawn prior to conversion colddrawing at this stage is not essential. To obtain the highest qualityproduct, however, further cold drawing should be applied. The preferredprocedure is to cold draw the filaments both before conversion(predrawing) and after conversion (afterdrawing). The degree to whichthe filaments are cold drawn after conversion will depend upon theextent, if any, to which they have been drawn prior to conversion. Ifthey have not received any prior cold drawing, the best results areobtained by cold drawing the filaments from 100 to 300%. If thefilaments have been predrawn, the afterdrawing should preferably be suchas to make the total cold drawing from 200 to 400%. The filaments shouldbe wet with a liquid having a mild swelling action thereon duringafterdrawing, suitable liquids being hydroxylated nonsolvents, such aswater and the lower boiling alcohols.

The next step in the process is the spontaneous crimping operation. Thisis eflected by releasing the tension on the drawn wet fibers andallowing them to dry in the relaxed condition, i. e., under low or zerotension. The tension should be released before the fibers are completelydry. During the drying of the released fibers they crimp spontaneouslygiving a wool-like product. A very high degree of crimp is introduced bythis unique process of crimping, so that the ratio of the straightenedlength of the fibers or yarns to their crimped length (crimp ratio) isgenerally between 2 and 4. The products can therefore be stretched to aremarkable extent before the crimps straighten out. The filaments alsoundergo some 10 to shrinkage in straight length during crimping.

The time required for the crimp to appear varies somewhat with thenature of the polymer,

the spinning conditions, the agent with which the th time interveningbetween drawing and relaxation, but most of all with the rate of drying.The rate of drying of course is dependent upon the temperature and thehumidity of the surrounding atmosphere. Crimping takes place at acritical stage in the drying which can be accelerated by various means,e. g., by heat, by passing a current of dry gas over ,the fibers, or by\washing the fibers with alow boiling water-miscible liquid. The crimpingtime may vary from a few seconds to several minutes or longer. Usu-,

ally the crimp begins to appear when the moisture or liquid content ofthe fibers falls below about 4% by weight of the fiber.

The second method for imparting spontaneous crimping properties tofilaments, exemplified by subsequent Examples V-IX, is carried out asfollows: The first step consists in spinning a synthetic fiber-formingpolyamide of relatively low or medium intrinsic viscosity, 1. e.,ranging from an intrinsic viscosity of 0.6 to 1.00, and preferablybetween 0.65 to 0.85, from melt at a temperature as low as is consistentwith smooth spinning, generally from 5 to 30 C. above the melting pointof the polymer mass. Thus, for polyhexamethylene adipamide, th linearcondensation polyamide derived from hexamethylenediamine and adipicacid, the preferred intrinsic viscosity and spinning temperature rangesare, respectively, 0.65-0.85 and 270-285" C.; for polydecamethyleneadipamide, 0.65-0.85 and 240- 255 C.; and for 6-aminocaproic acidpolymer, 0.65-0.85 and 225-245 C. Although filaments prepared in thismanner can be used directly in the crimping process without anysubsequent conversion step, a more highly crimped product is usuallyobtained if the filaments are allowed to age for at least a fewhoursbefore subjecting them to cold drawing and spontaneous crimping.

The next operation applied to filaments prepared by the special meltspinning operation described above is to cold draw them. The filamentsshould be wet with a liquid having a mild swelling action thereon,preferably an hydroxylated non-solvent such as water, when they are colddrawn. The degree of swelling required is quite small. For example,water which works very satisfactorily causes only 2.5% swelling, i. e.,a 2.5% increase in the dimensions of the filament. Although filamentsspun under the conditions just described will exhibit the phenomenon ofspontaneous crimping over the entire range of cold drawing, there is acertain range over which the finest crimp is obtained. Thus, forpolyhexamethylene adipamide, the optimum degree of cold drawing isbetween and 350%,

i. e., until the length of the drawn fibers will be 2.5 to 4.5 timesthat of the original undrawn filaments. However, if the cold drawing isdone in stages, it is possible to cold draw the filaments substantiallycompletely and obtain a product having good crimp and strength.

The next step, the spontaneous crimping operation, is carried out in amanner similar to that described for the first process. It consists indrying the cold drawn wet filaments in the reexceptionally good broughtabout in a number of ,ways.

this remarkable phenomenon results from a difference of strain betweenthe exterior and interior portions of the filaments. What apparentlytakes place when the filaments are dried in the relaxed condition isthat the filament shrinks and in so doing takes on a crimp in an eiIortto relieve the difference in strain. In other words, the exterior andinterior portions of the filaments appear to shrink to a differentdegree. (A very high degree of shrinkage occurs in drying thesefilaments, much higher than in the case of undrawn filaments ornon-crimping cold drawn filaments.) This difierence in strain betweenthe exterior and interior of the filaments can be For example, in theconversion method wherein filaments wet with a mild swelling medium arepassed rapidly through hot oil, this difference between the exterior andinterior of the filaments is probably brought about by a greaterswelling action at the surface of the filament than in the interior,because the time of contact in the oil bath is too short to efiectthorough penetration of heat. In the case of longer heat treatments orof heat treatments in the absence of a swelling medium, the whole of thefilament is probably affected more or less similarly and as a result thefilament must be cold drawn with the exterior and interior portions atdifierent moisture con tents to obtain the necessary non-homogeneousstrain for crimping. This is done by wetting the filament and colddrawing it while it is drying out. Spinning from melt under the specialconditions previously described also appears to give filaments which arenon-homogeneous or at least become so on subsequent cold drawing. Sincesynthetic linear condensation polymers are crystalline, this postulatedstrain or non-homogeneity between the outside and inside of thefilaments may be due to or relate to a difference in crystalline size orform. Owing to their crystalline character and their readysusceptibility to cold drawing, filaments of these polymers ofierunusual opportunities for bringing about this nonhomogeneity. No othertype of filament ofiers this opportunity.

The crimp produced in the fibers by the process of this invention islargely helical in character, although some fiat crimps (in one plane)may also be present. The fineness of the crimp, i. e., the number ofcrimps per inch, depends somewhat upon the conditions under which thecrimped fibers are prepared. It is not diflicult, however, to obtainproducts having thirty crimps per inch. Finely crimped fibers have 20 to40 crimps per inch. As already indicated, the fibers assume a helical orcurled form so that the fiber has the appearance of a coiled spring.These helices reverse their direction at irregular intervals, usuallyabout every 0.08 to 0.4 inch in the case of finely crimped products.This is a unique fiber is not under tension. When formed into a fabric,the reversing helical crimp in the fibers is not so readily apparent.

The crimp produced by the spontaneous crimping process is sufllcientlypermanent to permit the use of the product in many applications. Thepermanency of the crimp depends in a large measure on the treatment thefilaments have received prior to crimping. For example, filaments whichhave been subjected to conversion, e. g., by means of oil, have a higher"crimp recovery from stretc than filaments which have been renderedcrimpable by the special condition of high that the setting treatmentdescribed betype of crimp not possessed by any other known artificialwool. Fine crimps have helical diameters of 0.02 to 0.08 inch, whereasthe coarser crimps (4 to 6 crimps per inch) usually have helicaldiameters ranging from 0.15 to 0.3 inch. It should be understood thatthe helices are not perfeet and that their size and shape may varyconsiderably even within an individual fiber. In general at least fourcrimps per inch are required to obtain a truly valuable wool substitute.When reference is made to the number of crimps per inch it is to beunderstood that this refers to the number of crimps (complete turns) perinch in the fiber in its relaxed condition, i. e., when the low isunnecessary.

The crimp recovery from stretch of the polyamide fibers can be increasedto a very high value by heat treatment, particularly if the heattreatment, as in the following examples, is conducted in the presence ofwater or other suitable setting medium. Saturated steam at to 200 C. isparticularly effective. Thus, if crimped synthetic polyamide fibers areheated with saturated steam for thirty minutes at C., the crimpretentivity and the crimp recovery from stretch of the resultant fibersbecome practically as good as that of natural wool. Under certainconditions steam-treated polyamide fibers retain their crimp much betterthan does natural wool. For example, if the synthetic polyamide wool ofthis invention is stretched until the crimps are straightened out and anadditional 10% elongation is applied, and the fiber in this condition iskept for three days under ordinary conditions and then released,substantially all the crimp returns. If natural wool is stretched underthe same conditions and held only 15 hours, the crimp is substantiallycompletely destroyed. Moreover, on long immersion in hot water underthis degree of stretch, the synthetic polyamide wool retains its crimpmuch better than does natural wool.

As indicated in subsequent Example VI, a surprising degree of crimpsetting can be effected by treating the drawn filaments with boilingwater or steam before allowing them to crimp.

The following examples are illustrative of methods for practicing ourinvention:

Example I A 95-denier, lo-filament water-wet yarn prepared fromfilaments of polyhexamethylene adipamide (intrinsic viscosity 0.95),which had been drawn 100% while wet, was passed through a light mineraloil heated to 150 C. at such a rate that the time of contact wasapproximately one-quarter second. The oil was removed from the filamentsby washing with soap and water. The yarn was then further cold drawnwhile still wet. The yarn was next centrifuged, washed with acetone, andpassed through squeeze rolls to remove excess acetone and retainedwater. From the squeeze rolls the acetone-wet yarn was taken by an airaspirator which injected the yarn at a rate of 1200 ft./min. into thetop of a vertical column 9 feet long and 3 inches in diameter. A currentof air just insufficient to support the weight of the yarn was passed upthe column. Under these conditions the yarn dried in the column andcrimped spontaneously. On reaching the bottom of the column the crimpedyarn was laid down on a moving endless belt traveling slower than therate at which the yarn was laid down, so that the crimp was preserved.The belt carried the yarn through a horizontal tube filled withsaturated steam at 100 C. The length of this tube was such that the yarnwas in contact with steam for approximately 20 seconds. On leaving thesetting tube the yarn was wound on a bobbin. It had a crimp retentivityof 100%, a crimp recovery from stretch of 60% and a tenacity of 1.6 g.

per denier based on the denier of the crimped yarn when straightened.Longer heating with steam was found to increase the crimp recovery fromstretch.

Example II An undrawn 100-denier, 10-filament yarn of polyhexamethyleneadipamide 'of intrinsic viscosity 0.95 was wound on a bobbin and treatedwith saturated steam for three minutes at 150 C. After cooling the yarnwas moistened with water, dried partially, cold drawn 150% while dryingout, and collected on a bobbin which was kept wet. The wet yarn was thenreleased and allowed to dry further, whereupon it crimped spontaneously.After setting with steain the yarn had good crimp recovery from stretch.

Example III An undrawn 300-denier, 30-filament yarn of polyhexamethyleneadipamide of intrinsic viscosity 0.86 was soaked in water, cold drawn200%, and collected on a bobbin. The yarn was dried on the bobbin (1. 0.while under tension) and then soaked in methanol for about 15 minutes.The methanol-wet yarn was passed from the bobbin at a rate of 100ft./min. through a sixinch bath containing tetrachloroethylene at 105 C.On leaving the bath the yarn was wound on a bobbin and allowed to standuntil substantially free from tetrachloroethylene. The bobbin was thensoaked in water and the yarn cold drawn 40%. The yarn was centrifugedand washed with acetone to remove the major portion of the water. Theacetone-wet yarn was next led at a rate of 1200 ft./m1n. through squeezerolls and then by means of an air aspirator into the top of a verticalcolumn 9 feet long and 3 inches in diameter. The function of theaspirator was to direct the yarn away from the squeeze roll and into thevertical column. In this column the yarn dried and crimpedspontaneously. On leaving the crimping column, the yarn was wound in asuitable package. The product had very high crimp, the ratio of straightlength to crimped length being about 3.5. Moreover, the yarn hadexcellent crimp recovery from stretch (95%) so that no subsequentsetting was necessary.

Eccample IV An undrawn 240-denier, 30-filament yarn of polyhexamethyleneadipamide was soaked in water and then passed at a rate of 50 ft./min.through a capillary tube 4 feet in length and 0.014 inch in diameterheated to 180 C. The converted yarn was then soaked in water again, colddrawn 150%, and wound on a skein reel. The wet yarn was removed from theskein, washed with acetone, and dried under low tension. The crimpedyarn obtained in this way was set by treatment with saturated steam at120 C. for 20 minutes. The product had a high degree of crimp andexcellent crimp retentivity.

Example V The polymer used in this example was viscosity stabilizedpolyhexamethylene adipamide having an intrinsic viscosity of 0.73, adensity of about 1.1, and a melting point of 263 C. as determined in aglass tube in the absence of oxygen (248 C. when tested on heated blockin air). mer was formed into filaments by extruding the molten polymer(temperature about 277 C.) under 70 lb. per sq. in. oxygen-free nitrogenpressure through a spinneret having 10 orifices each 0.0078 inch indiameter. The filaments thus formed, under the cooling action of the airinto which the polymer was extruded, were collected on a bobbin at arate of 583 ft./min. The denier of the individual filaments was about22. After 24 hours aging at ordinary temperature, the

vbobbin containing the undrawn 10-filament thread was soaked in waterand the thread cold drawn by winding it under tension on a second bobbinhaving a peripheral speed 3.5 times that of the first bobbin. Thisreduced the denier of the filaments to 6.0. The wet thread passed aroundthe drawing bobbin once and was then immediately released. The releasedthread was taken from the drawing bobbin by means of an air aspirator;the thread passed into the vacuum side of the aspirator and out what isnormally the air outlet tube. The thread then passed downward through aheated metal tube (inside air temperature about C.) which was five feetin length and had a gentle downward draft of air passing through it tocounteract the chimney efiect. After traveling down the tube thecritical point of drying was reached near the bottom. At this pointspontaneous crimping occurred with the formation of a wool-like threadcomposed of fibers having a reversing helical crimp. On leaving the tubethe crimped thread was wound loosely on a suitable bobbin.

In order to obtain low tension during winding, the thread as it left thetube was passed through a ring of glass which was perforated with alarge number of holes through which a stream of air was passed. Thethread tended to float through the middle of this ring and was guidedonto the bobbin and traversed by the motion of the ring. The bobbincontaining the crimped wool-like thread was then heated for 20 minutesat 120 C. in the presence of saturated steam to set the crimp. Thethread obtained in this way had a "crimp retentivity of practically anda crimp recovery from stretch" of 82%, a tenacity of about 4 g. perdenier based on the denier at break, and more than ten crimps per inchin the relaxed state.

The above thread was knitted into a fabric as follows: Six threads (10filaments each); were twisted together four turns per inch right andthen plied with a similar thread three and a half turns per inch left.Although the final denier of this wool-like yarn was about 1000, it hadapproximately the same diameter and bulk as a wool yarn of about 2500denier. The synthetic yarn was knit into a piece of fabric by hand. Thefabric obtained looked very much like a similar fabric knitted fromnatural wool yarn, i. e., it had excellent softness and an openness ofstructure resembling that of the wool The P y? fabric. The wool-likeproperties were not destroyed by washing in water. In a similar way awool-like polyamide fabric was prepared on a circular knitting machineusing a four-thread (tenfilaments each) yarn which has been twistedtogether ten turns per inch right under tension and plied with a similaryarn. This product resembled a similarly knitted wool fabric.

Example VI The filaments used in this example were prepared frompolyhexamethylene adipamide of intrinsic viscosity 0.74 in a mannersimilar to that described in Example V. These. filaments, which had adenier of about 13, were soaked in water for several hours. They werethen cold drawn 175% giving fibers having a denier of 4.7. While stillwet the fibers were treated on a bobbin with boiling water (settingagent) for 30 minutes. They were then removed from the bobbin and dried.The released fibers crimped spontaneously during drying, yieldingwool-like fibers having reversing helical crimps (30 crimps per inch).The crimped fibers were then treated for 2 minutes with air at 130 C.The crimp recovery from stretch of these fibers was approximately 90%,whereas crimped fibers similarly prepared but not subjected to asetting, treatment at any stage in their preparation had a crimprecovery from stretch of less than 10%.

Example VIl Viscosity stabilized polydecamethylene adipamide ofintrinsic viscosity 0.74 and melting point 238 C. (in absence of oxygen)was spun from melt at approximately 245 C. under a pressure of 160lb./sq. in. The spinning rate was 600 ft./min. After aging for sometime, the filaments thus obtained were wet with water, cold drawn 175%,relaxed while still wet, and dried. The crimp appeared in the relaxedfibers within 20 seconds without forced drying. The ratio of straightlength to crimped length of the fibers was approximately 2. Heating therelaxed fibers accelerated the appearance of the crimp, but thisprocedure gave fewer crimps per inch. The crimp was set in these fibersby heating them in saturated steam at 120 C. for 20 minutes. Theresultant synthetic wool had a crimp retentivity" of approximately 100%and a crimp recovery from stretch of 76%. The individual fibers had adenier of 5.2, a tenacity of 2.5 g. per denier based on the denier atbreak, and a residual elongation of 121%.

Example VIII A 60-filament, 2.7-twist per inch yarn, prepared fromundrawn filaments obtained by melt spinning ,polyhexamethylene adipamideof intrinsic viscosity 0.75 at approximately 277 C., was moistened withwater and cold drawn 175%. The drawn yarn was then wound on a skeinreel, the yarn being kept wet during the winding. The yarn was nextremoved from the reel, dipped twice in acetone, and allowed to dry. Onevaporation of the major portion of the acetone and retained water, thefibers in the skein crimped spontaneously. The crimps were of thereversing helical type. Some fibers contained more crimps per inch thanothers, but the majority had from 20 to 40 crimps per inch. Steam wasblown over the skein for a short time and then the skein was given a 20minute setting treatment by placing it in saturated steam at 120 C. Theskein was placed on a swift and unwound onto a twisting machine wherethe yarn was given 2.7 twists per inch. The yarn had a denier of 270 anda tenacity of 1.3 g. per denier based on the initial denier.

A yarn of this type was woven into a fabric using 60 threads per inch ofspun rayon (2 ply 36's) as warp and the polyamide wool yarn as fillingusing a 2/2 twill 48 picks per inch weave. Another fabric was thenprepared in a similar way using in place of the polyamide yarn a 1/27's(295 denier) worsted yarn. The fabrics were then given a finishingtreatment which consisted in tentering followed by decatizing using 55pound pressure steam on the drum for 10 minutes and 10 minutes dryingand cooling by evacuation. The fabrics were then scoured, starting withcold water and heating to about 50 C. using a detergent for 30 minutes,followed by a hot water wash (50 C.) of 15 minutes, and a 20 minutebleaching treatment with peroxide at 50 C. After being washed again inhot and cold water, the fabrics were dried in a centrifugal wringer anddried in a hot air drier. They were then tentered for a second time. Thepolyamide-filled fabric compared favorably in appearance and feel withthe worsted-filled fabric. The polyamide fabric was readily dyed.Moreover, it could be dyed without ill effect with indigo and thesulfanthrene type dyes with a concentration of alkali and hydrosulfitewhich was damaging to the worsted-filled fabric.

Example IX Polyhexamethylene adipamide of intrinsic viscosity 0.81 wasspun into filaments in a manner similar to that described in Example V.The filaments, which had a denier of 18 each, were collected on abobbin, aged for some time, immersed in water, and drawn The wetfilaments were redrawn 150%, which is equivalent to a total of 400% colddrawing based on the original length. On relaxing the drawn filamentsand allowing them to dry, they crimped spontaneously, yielding highlywool-like fibers having approximately 20 crimps per inch, a ratio ofstraight length to crimped length of 3.5, and

' a tenacity of about 5 g. per denier based o the denier at break.

Although this invention has been described with particular reference topolyamides, it is applicable broadly to fiber-forming synthetic linearcondensation polymers. To obtain products useful in the textile field,however, the melting point of the polymers should be above C. so thatthey can be washed with boiling water. The most useful products areobtained from polymers having a melting point above 220 C. As examplesof fiber-forming synthetic polymers might be mentioned polyesters,polyanhydrides, polyacetals, polyethers, polyester-polyamides, and otherco-polymers. The preparation of polymers of this class is described indetail in the patents referred to above.

The fiber-forming polyamides or superpolyamides described in the abovementioned patents and in application Serial Number 74,811 are the mostuseful of the linear condensation polymers for conversion into thewool-like products of this invention. Of these polyamides a valuableclass for use in the preparation of wool-like fibers comprises thosederived fromdiamines of formula NH2CH2RCH2NH2 and dicarboxylic acids offormula HOOCCHzR'CHzCOOH or their amideforming derivatives, in which Rand R are divalent hydrocarbon radicals free from olefinic andacetylenic unsaturation and in which R has a chain length of at leasttwo carbon atoms. An especially valuable group of polyamides within thisclass are those in which R is (CH2): and R is (CI-12);, wherein a: and yare integers and a: is at least two. As examples of polyamides whichfall within one or both of these groups might be mentionedpolytetramethylene adipamide, polytetramethylene suberamide,polytetramethylene sebacamide, polypentamethylene sebacamide,polyhexamethylene adipamide, polyhexamethylene B-methyl-adipamide,polyhexamethylene sebacamide, polyoctamethylene adipamide,polydecamethylene adi-pamide, polydecamethylene pphenylene diacetamide,and poly-p-xylene sebacamide. This invention is also applicable tofiber-forming polyamides derived '"om polymerizablemonoaminomonocarboxylic acids or their amide-forming derivatives, suchas S-aminocaproic acid, 9-aminononanoic acid, and 11- aminoundecanoicacid. Thus, application of the process of Example V to a viscositystable polymer of intrinsic viscosity 0.72 obtained from 6- aminocaproicacid gave a wool-like product having between 30 and 40 crimps per inch,a "crimp recovery from stretch of 78%, and a tensile strength of 4.3 g.per denier based on the denier at break. It is also within the scope ofthis invention to prepare wool-like fibers from mixtures of preformedpolyamides and from interpolymers or co-polymers derived from a mixtureof polyamide-forming reactants, e. g., a mixture of two diamines withone or more dicarboxylic acids, or a. mixture of a diamine, adicarboxylic acid, and an amino acid.

While the wool-like polyamide fibers of our invention are in generalless lustrous than unto crimping in a readily volatile liquid likeacetone which is miscible with the swelling agent present. The acetonereplaces the water or other swelling agent present and thus hastens thedrying operation and the appearance of the crimp. Examplesof otherliquids which can be used in place of acetone are methyl alcohol, ethylalcocrimped polyamide fibers, their luster can be modified or destroyedby the addition of suitable luster-modifying agents, such as titaniumdioxide and other pigments. Thus the application of the process ofExample V to a polyamide containing 2% of titanium oxide gave adelustered wool-like product containing more than 20 crimps per inch, acrimp recovery from stretch of 65%, and a tensile strength of 3.5g. perdenier based on denier at break. The delusterant may be added to thepolyamide before or after (surface delustering) it is converted intowool-like fibers. Preferably, it is incorporated in the polyamide beforeit is formed into fibers. It is also possible to carry out the processof our invention using polyamides containing other types of materials,e. g., plasticizers, resins, oils, cellulose derivatives, fillers,pigments, dyes, antioxidants, etc. If a plasticizer is used, it may beremoved before or after the crimping operation or it may be retained inthe final product.

It is evident from the foregoing discussion and examples that aconsiderable degree of latitude is permitted in the mode in which theinvention may be practiced. The process can be carried out as a batchprocess (e. g., Example V) or as a continuous process (e. g., ExampleI). The filaments can be crimped while moving through a drying chamber(Example I) or they can be crimped while in a stationary position, e.g., in skein form (Example VIII). Similarly the setting operation can beapplied in a continuous or batch process. If desired, the settingoperation, e. g., with hot water or steam, can be applied before thecrimp is formed (Example VI), but preferably it is applied after thecrimp is introduced (Example V).

As indicated in a number -of the examples, the wet fibers can, ifdesired, be soaked prior hol, isopropyl alcohol, methyl ethyl ketone,ethyl ether, dioxan, ethyl acetate, as well as mixtures of variousreadily volatile liquids. If the swelling agent is itself readilyvolatile, e, g., methanol, this step is unnecessary.

In the process of this invention it is important that the cold drawnfibers which are ready for crimping be kept moist as long as they areheld under tension. However, if the fibers contain a suitable wettingagent, e. g., a sulfurized oil, they may be dried while under tensionand be made to crimp by wetting them with water or other swelling agentand then releasing the tension thereon. When the relaxed fibers dry,they crimp spontaneously but in general the crimp obtained in this wayis not so good as that obtained from fibers which are kept wet duringthe entire periodthey are susceptible to crimping.

While heating with steam is the preferred method of setting, it iswithin the scope of this invention to set the crimp in the fibers byother wet heat treatments. For example, hot liquids and vapors whichhave a mild swelling action on the fibers, 'e. g. methanol, function assetting agents. Hot water or dilute aqueous solutions of phenol orformic acid may be also employed. In fact, it is possible to use' hotaqueous solutions of a large variety of materials which do not degradeor dissolve the fibers in the concentration used. Some degree of settingcan also be effected by heating the filaments while dry, e. g., at IOU-C.

While the process of this invention is applicable to filaments ofsynthetic linear condensation polymers generally, it will be apparentthat the optimum operating conditions will vary somewhat with differentfilaments depending upon their properties and the manner in which theywere prepared and treated. The optimum conditions for each polymer canbe worked out experimentally, the essential features of the processbeing those outlined above.

The wool-like filaments obtained in accordance with this invention canbe formed into yarns and fabrics by conventional methods with or withoutthe addition of other filaments. Valuable yarns are obtained by plyingfilaments having different crimp ratios. A very useful method forforming plied yarns consists in feeding two strands of crimped filamentsinto a twister at different rates. This gives a yarn in which somefilaments (the strand fed at the more rapid rate) have a longer straightlength than the remaining filaments. This is desirable since the c-rimpsdo not all pull straight at the same time when tension is applied to theyarn. A novel method for securing the same effect is to ply two strandsof filaments, one strand of which has been crimped and the other strandwhich is wet and capable of crimping on drying. After plying the yarn isdried whereupon the uncrimed strand crimps. Since the latter strandshrinks during crimping, a highly crimped yarn is obtained in which thefilaments have different straight lengths and hence do not all pullstraight at the same time under tension. Such yarns give especiallywool-like fabrics.

The fibers of the foregoing examples are continuous. If desired, thesewool-like continuous fibers can be cut into short lengths, e. g., one tosix inches, and these staple fibers formed into yarns and fabrics withor without the addition of other types of staple fibers. Fabricsprepared in this way have a more fuzzy appearance and feel than thoseprepared from the continuous fibers. It is also possible to preparestaple woollike fibers by cutting the moist cold drawn con tinuousfibers before crimping, in which case the crimping occurs in the staplefibers. Another method for preparing wool-like staple fibers consists indrawing wet filaments capable of crimping until they break and then.drying the broken filaments to permit crimping. It is also possible todraw a bundle of filaments so as to break them into shorter lengthswithout destroying their parallel arrangement thus obtaining a sliverready for spinning without the necessity of carding. Useful yarns canalso be obtained by drawing a plurality of filaments until only. some ofthe filaments break.

Our new crimped polyamide fibers possess in addition to the desirableproperties of natural wool the valuable properties characterizing thestraight polyamide fibers. They show, for instance, fiber orientationwhen examined by Xrays. They have good resistance to solvents andchemical reagents. On heating with strong mineral acid, however, thewool-like fibers disintegrate yielding the monomeric ingredients fromwhich they were derived. Thus, if polyhexamethylene adipamide wool isheated with hydrochloric acid, it is hydrolyzed slowly yielding adipicacid and hexamethylene diamine (as the hydrochloride). The fibers areresistant to attack by strong caustic alkalies, but these agencies alsowill finally hydrolyze them.

The wool-like polyamide products of this invention have wet strengthssubstantially equal to their dry strengths. The tenacity of the fibersgenerally range from 1.2 to 4 g. per denier based on the initial denier,which 'is considerably greater than that of natural wool. Owing to thegreat strength of our new synthetic wool, fine waips and fillings can bemade: therefrom. This makes it possible to prepare fabrics of very finethread counts (sheers) from our synthetic wool whichis not possible inthe case of natural wool. The products of this invention can be dyedwith the dyes used for wool. Unlike wool, the polyamides can be dyedwithout significant deterioration with dyes which are used in analkaline medium. Moreover. the polyamide wool fibers and fabrics havegood heat insulating properties. Since the polyamide has a lower densitythan wool, fabrics made therefrom are lighter than wool fabrics.

From the foregoing description it will be seen that this inventionprovides a convenient and economical process for the preparation of highquality artificial wool-like fibers. The outstanding feature of theprocess is the spontaneous crimping and the outstanding feature of theproduct is its unusually high crimp permanency. The products, in thecase of the polyamides at least, are approximately equal to natural woolin crimp retention and heat insulating properties, and are superior towool in strength, dyeing characteristics, heat stability, uniformity ofcharacteristics, freedom from shrinkage, and low moisture regain. Unlikewool they are not attacked by moths. The artificial wool-like productsof this invention are thermally stable at 150 0., whereas natural wooldecomposes quite rapidly at this temperature with liberation of ammonia,hydrogen sulfide, and carbon bisulfide. The process by which theartificial fibers of this invention are made is of such character thatmodifying agents, for example, delusterants and plasticizers, can bereadily incorporated therewith. As already indicated, the fibers of thisinvention whether long (continuous) or short (staple) can be easilyformed into yarns. Thus it is possible to prepare yarns of the worstedtype from these fibers. The yarns can be knitted or woven into fabrics,rugs, and the like. If desired, other types of fibers (continuous orstaple, straight or crimped) or yarns, e. g., viscose rayon, acetaterayon, cotton, silk, linen and wool, can be used in conjunction with thecrimped synthetic polymer fibers or yarns in the preparation of mixedfabrics" as described more fully for the polyamide wool covered in theabove mentioned co-pending application by J. B. Miles, Jr. Straightsynthetic polymer fibers and yarns as well as the crimped polymer fibersof the .copending Miles application can also be used with the productsof the present invention. Interesting felt-like fabrics can be preparedby bringing together in a compact layer a large number of wet syntheticpolymer filaments, which are capable of spontaneous crimping, andallowing them to dry and crimp in this position so that the crimpsintertwine thereby holding the fibers together in a mosaic-like web. Theproducts of this invention are also useful as down substitutes and asstufiing material for upholstery, pillows, and comforters. They can alsobe used in making felted articles, e. g., hats. In contrast to otherknown synthetic wools, the polyamide products of this invention do notlose their crimp on wetting and drying. This is a highly desirableproperty. A bundle of crimped polyamide fibers when wet and squeezedwill spring back instead of remaining packed as will crinkled or crimpedcotton, viscose rayon, cellulose acetate rayon, or any other known woolsubstitute. This is also true of the corresponding fabrics.

As many apparently widely different embodiments of this invention may bemade without departing from the spirit and scope thereof, it is to beunderstood that we do not limit ourselves to the specific embodimentsthereof except as defined in the appended claims.

We claim:

1. A synthetic linear polymer in the form of a crimped fiber which showspronounced crystallinity and orientation along the fiber axis whenexamined by X-rays and whose crimps are preponderantly helical.

2. An artificial fiber which consists essentially of synthetic linearpolymer and which has at least 4 crimps per inch and a crimp retentivityof at least 40%, said crimps being preponderantly in helices whichreverse their direction at intervals along the fiber. said crimpretentivity being determined by applying 10% stretch to the straightenedfiber, immersing in boiling water for 30 seconds, and drying in relaxedcondition.

3. A synthetic linear condensation polymer in the form of a crimpedfiber having its crimps preponderantly in helices.

4. A synthetic linear polyamide in the form of a crimped fiber having atleast 4 crimps per inch and having its crimps preponderantly in heliceswhich reverse their direction at intervals along the fiber,

5. The fiber set forth in claim 4 in which said polyamide derived from adiamine of formula NHzCHzRCHzNI-Iz and a compound of the classconsisting of dicarboxylic acids of formula HOOCCHzR'CHzCOOH andamide-forming derivatives thereof, in which R and R are divalenthydrocarbon radicals and in which R has a chain length of at least twocarbon atoms. 1

6. A synthetic linear polyamide in the form of a crimped staple fiberhaving its crimp preponderantly in helices.

7. A textile material of the class consisting of wool-like yarns andfabrics which comprise synthetic linear polyamide fibers having ahelical crimp.

8. A wool-like yarn comprising synthetic linear polyamide fibers whichare capable of undergoing cold drawing and which possess a helicalcrimp.

9. A fiber possessing a helical crimp, said fiber comprising essentiallya material which yields on hydrolysis with mineral acid a diamine and adibasic carboxylic acid- 10. A process for preparing a crimped fiberwhich comprises cold drawing a synthetic linear condensation polymerfilament which is swollen by a mild swelling agent and in which theexterior and interior portions tend-to shrink to a different degree,releasing tension on the filament, and removing the swelling agent bydrying thereby causing the filament to crimp.

11. A process for producing a wool-like product which comprises spinninga filament from a molten synthetic fiber-forming polyamide, wetting thefilament with a mild swelling agent, partially cold drawing the wetfilament, releasing tension thereon, and drying the relaxed filament toremove the swelling agent.

12. A process for producing crimped fibers which comprises spinning afilament from a molten mass of synthetic linear condensation polyamideof intrinsic viscosity 0.6 to 1.00 at a spinning temperature of 5 to 30C. above the melting point of the polyamide mass, wetting the filamentwith an hydroxylated non-solvent for the polyamide, cold drawing thefilament 50% to 300% while wet, releasing tension on the wet filament,drying it, and setting the crimp resulting therefrom by treatment withsaturated steam at a temperature of 100 to 200 C.

13. In the manufacture of a wool-like product from a syntheticfiber-forming polyamide, the steps comprising heating a filament derivedfrom said polyamide, wetting the filament with a liquid having a mildswelling action thereon, cold drawing the wet filament, releasingtension on the wet filament, and allowing it to dry thereby causing itto crimp.

14. In the manufacture of a wool-like product from a syntheticfiber-forming polyamide, the steps comprising wetting a partially colddrawn filament derived from said polyamide with a liquid having a mildswelling action thereon, passing the wet filament rapidly through a bathcontaining a hot liquid non-solvent for the polyamide, further colddrawing the filament while wet with a liquid having a mild swellingaction thereon, and drying the filament in the relaxed condition.

15. In the manufacture of wool-like products from synthetic linearcondensation polyamides, the steps comprising wetting with waterfilaments comprising said polyamides, heating the water-wet filaments inmineral oil at a temperature of about 140 C. to about 165 C. for about0.5 to about 0.2 second, washing the filaments to remove retained oil,cold-drawing the filaments while wet with water, and drying thefilaments in a relaxed condition.

16. In the manufacture of wool-like products from synthetic linearcondensation polyamides, the steps comprising wetting filamentscomprising said polyamides with methanol, heating the wet filaments intetrachloroethylene at a temperature of about 100 C. to 110 C. for about0.4 to 0.2 second, removing the major portion of thetetrachloroethylene, wetting the filaments with water, cold drawingthem, and then drying the filaments in a relaxed condition.

17. A process for manufacturing a wool-like product from filaments ofsynthetic polyamide which includes the steps of wetting the filamentswith a mild swelling agent therefor, cold drawing the wet filaments,releasing tension on the drawn wet filaments, and then drying thefilaments in relaxed position.

18. A process for producing a wool-like prodduct which comprisesspinning a filament from a molten synthetic fiber-forming polyamide at atemperature as low as is consistent with smooth spinning, wetting thefilament with a mild swellswelling agent.

19. A down substitute suitable for stuffing upholstery, pillows and thelike which comprises a synthetic linear condensation polymer in the formof a crimped fiber having its crimps preponderantly in helices.

20. The process of treating a synthetic yarn which comprisesimpregnating the yarn with a relatively low boiling swelling agent anddisplacing the swelling agent by a relatively high boiling lubricatingagent maintained at a temperature at which the swelling agent has a highvapor pressure.

21. The process of treating a textile yarn which comprises impregnatingthe yarn with a relatively low boiling swelling agent and displacing theswelling agent by a relatively high boiling lubricating agent maintainedat a temperature at which the swelling agent has a high vapor pressure.

22. The process of treating a synthetic yarn which comprisesimpregnating the yarn with a relatively low boiling swelling agent, andthen treating the yarn with a relatively high boiling lubricating agentat a temperature at which the swelling agent has a high vapor pressure.

23. The process of treating a textile yarn which comprises impregnatingthe yarn with a relatively low boiling swelling agent, and then treatingthe yarn with a relatively high boiling lubricating agent at atemperature at which the swelling agent has a high vapor pressure.

24. The crimped fiber set forth in claim 9 in which said polyamide ispolyhexamethylene adipamide.

25. The process set forth in claim 12 in which said polyamide ispolyhexamethylene adipamide.

26. The process set forth in claim 17 in which said polyamide ispolyhexamethylene adipamide.

2'7. The process set forth in claim 21 in which said yarn comprises asynthetic linear polyamide.

28. The process set forth in claim 22 in which said yarn comprises asynthetic linear polyamide.

29. The crimped fiber set forth in claim 4 in which said polyamidecomprises a polymerized monoaminomonocarboxylic acid.

VERNAL R. HARDY. JOHN B. MILES, JR.

